Backlighting for active matrix liquid crystal displays (“AMLCD”) typically uses a cold cathode fluorescent lamp (“CCFL”) device. CCFL devices tend to have high back lighting efficacies. CCFL devices have numerous drawbacks. CCFL devices may contain Mercury, a highly dangerous substance that has been banned from many AMLCD applications. CCFL devices may have poor efficacy at lower temperatures, which requires additional circuitry such as a heater element or a boost current circuit. CCFL devices may have a non-linear efficacy curve with respect to temperature. CCFL devices may require an inverter to drive the CCFL device. CCFL devices may require complex control schemes, including light sensors and temperature sensors to provide adequate dimming ratios for night time operations. CCFL devices may have a short life expectancy, especially at lower operating temperatures, and may require additional electro-magnetic interference (“EMI”) shielding and electric filtering.
Alternatives to CCFL devices for back lighting an AMLCD include Xenon-based devices. Xenon-based backlighting circuits do not contain Mercury, have superior low temperature life expectancy and low temperature operational characteristics, and have less phosphor degradation than CCFL devices. While Xenon lamps correct many of the problems of the CCFL lamp technology, the Xenon lamp technology creates many new problems. For example, Xenon lamps tend to be relatively expensive and require complex control circuitry. Xenon lamps have low efficacy. For example, a Xenon lamp with twice the diameter may provide only half the brightness of a mercury-based CCFL lamp. Because the efficacy of the Xenon lamp may be less than half of a CCFL lamp, the additional power needed to power a Xenon based circuit creates a problem of power consumption.
Another alternative to CCFL devices for backlighting are white LEDs. White LEDs have been used to provide light to light pipes in LCD backlighting devices. White LEDs may be more expensive than colored LEDs.